The objectives of this research project are to determine the role of surgery in the treatment of atrial dysrhythmias. First, the surgical anatomy and physiology of the atria will be defined by various surgical procedures. For example, the following will be done: excision or exclusion of the SA node from the remainder of the atrium; separation of the coronary sinus from the remainder of the atrium; the sequential division of the internodal tracts; division of Bachman's Bundle and excision of the atrial septum. The feasibility will be explored of substituting coronary sinus or AV nodal rhythm for defective SA nodal rhythm. The production of atrial rhythm disturbance will be done to determine whether or not any of the experimental surgical procedures can be employed for clinical use. The response of the atrium and heart after the above procedures to isoproterenol, atropine and parasympathetic and sympathetic nerve stimulation will be investigated.